A flat panel display (FPD) typically comprises a glass or a glass like substrate having an array of thin-film transistors formed thereon. To form the array, the substrate is subjected to various high temperature processing steps (e.g., chemical vapor deposition), many of which also require corrosive gases. Typical temperatures for chemical vapor deposition (CVD) processes can reach about 300xc2x0 C. or higher. At these temperatures a substrate is at risk of experiencing non-uniform processing which can degrade display quality. Specifically, in order to process uniformly across its entire surface, a substrate must be flat during processing. Thus, non-uniform processing may occur when the platform that supports the substrate deforms, causing the substrate to deform therewith. Platforms that support substrates during processing are conventionally known as susceptors, and are conventionally made of aluminum because of aluminum""s excellent corrosion resistance when exposed to CVD processing chemicals. The strength of aluminum, however, begins to decline rapidly above 150xc2x0 C. In fact, aluminum begins to soften at 250xc2x0 C. and exhibits xe2x80x9cliquidxe2x80x9d type properties at about 660xc2x0 C. Thus, when exposed to typical CVD processing temperatures, aluminum susceptors may deflect (e.g., bend or droop at the edges when supported at the center as is conventional). Such deflection is further exacerbated by the current trend toward larger and larger display sizes. Current display sizes are about 550 mmxc3x97650 mm, and are projected to reach well above a square meter in the near future. As display size increases, so does susceptor size and the deflection associated therewith.
Accordingly, a susceptor that resists deflection during high temperature processing is needed.
In one aspect the present invention provides a susceptor having a substrate supporting surface and an internal support frame that provides mechanical strength in a plane orthogonal to the substrate supporting surface, and provides flexibility in a plane parallel to the substrate supporting surface. The inventive susceptor may comprise a stainless-steel (or some other high strength material or compound) internal support frame that is cast within aluminum. Thus, the aluminum forms the substrate supporting surface. In this aspect the support frame is configured in a design that provides open areas in the plane parallel to the substrate supporting surface (i.e., in the plane parallel to the substrate supporting surface the support frame is not solid). The design may comprise, for example, a plurality of multi-sided shapes having straight and/or curved sides. Exemplary designs may comprise a honeycomb or wave pattern, as further described below. When the internal support frame is cast within aluminum, the aluminum occupies the open areas defined by the stainless-steel support frame.
The internal support frame may comprise one or more thin stainless-steel xe2x80x9ccomponentsxe2x80x9d or xe2x80x9cmembersxe2x80x9d that have a larger dimension in the plane orthogonal to the substrate supporting surface, than in the plane parallel to the substrate supporting surface. Thus the members are more flexible in the plane parallel to the substrate supporting surface, than they are in the plane orthogonal to the substrate supporting surface.
Other features and aspects of the present invention will become more fully apparent from the following detailed description of the preferred embodiments, the appended claims and the accompanying drawings.